Surgery requiring general anesthesia for oral, maxillofacial and some throat procedures require the patient be intubated nasally so the surgeon has access to the respected surgical site.
One significant problem with nasal intubation is it is very difficult to pass the desired sized endotracheal tube through the nasal passage. The clinician usually has to use a smaller than desired endotracheal tube to pass through the nasal anatomy. The problem with this fact is the endotracheal tube will be too small to properly fit the larynx, and thus too large of an air leak will be present around the tube. Too large of an air leak around the endotracheal tube would result in insufficient pressure in the pulmonary tree, thus making it very difficult, if not impossible, to ventilate the patient. If the patient is not properly ventilated, it is difficult to maintain the appropriate saturation levels of oxygen and anesthetic gases.
Another problem with a nasal intubation is that the open beveled distal end of an endotracheal tube can traumatize the anatomy of the nasal passages and the tissue of the adenoids. Many times the nasal endotracheal tube will remove adenoidal tissue which can occlude the lumen of the nasal endotracheal tube and/or produce a bleed from the tissue in question.
A nasal endotracheal tube can also tunnel through and along the posterior wall of the nasopharynx which will also result in an occluded lumen of the endotracheal tube and may also produce a bleed or swelling of the tissue. The result of this wound could not become apparent until after surgery and could be life threatening. Blood and tissue may not make an occlusion of the nasal endotracheal tube apparent until well into a procedure when blood would clot within the tube. This would raise a patient's carbon dioxide level and lower their oxygen saturation level, which could also lead to morbidity and mortality. The nasal endotracheal tube can also damage the turbinate bones in the nasal passages. There have been documented cases of these turbinates being avulsed and even aspirated into the pulmonary tree. An avulsion of the middle turbinate can expose the floor of the cranial vault and can leak cerebral spinal fluid.
Bleeding from the pharyngeal region can also trigger a laryngospasm. This occurs when fluid (i.e. blood) makes contact with the vocal cords. If a patient is in a certain stage of anesthesia and protective reflexes are not intact then the vocal cords if stimulated by a fluid may spasm and close, thus losing the airway. This could result in death, or central nervous system damage. If blood is introduced into the pulmonary tree (i.e., aspirated) then a post-operative pneumonia may also develop.
An endotracheal tube may also may carry and introduce microbes from the nasal passages into the pulmonary tree. This may again lead to pneumonia.
The article Elwood et al., Nasotracheal Intubation, A Randomized Trial of Two Methods, Anesthesiology 2002:96; 51-3 discloses an evaluation of red rubber catheters as a guide to nasotracheal intubation. In the trial children presented for elective surgery were randomized to undergo red-rubber catheter-guided nasotracheal intubation or to have the nasotracheal tube alone inserted. The results were that age, weight, snoring history, and difficulty of intubation were not different between the groups. Obvious bleeding was lower using the red-rubber catheter technique, which took longer to perform.